This invention relates to gaskets for sealing joints between parts containing fluid, such as between flanges of pipes and the like, and in particular to such sealing where the chemical and/or physical properties of the fluid presents a particular danger should leakage occur from the joint.
An example of such a sealing problem is between flanges of pipes or the like containing a flow of hydrofluoric acid (HF) at elevated temperature and pressure.
Because of the aggressive nature of the acid, both as a corrosive chemical, a turbulent fluid and an electrolyte, existing gaskets may be susceptible to attack by the acid and thus not considered to be completely satisfactory in providing flange joints with both the degree of sealing and security over a period of time considered desirable for safe operation.
Such a situation of security with respect to containing difficult chemicals under unfavourable physical conditions is not confined to this medium alone and the situation has parallels elsewhere.
It is known from patent specification GB-A-2066383 to provide a spiral gasket arrangement including, in addition to a spiral wound element, radially outward and radially inward solid supporting rings, the former being intended to act as a compression stop for the flanges and the latter being enclosed within a coating of elastomer material, particularly neoprene rubber, to provide a resilient seal between facing flanges to prevent liquid contained in the pipes from passing between the flanges and supporting ring to the spiral wound gasket element.